Thermostats for internal combustion engines are known, and are generally operable to control the flow of coolant fluid through the engine and associated engine cooling system based on coolant fluid temperature. Conventional thermostats have a closed position for inhibiting the flow of coolant fluid through the engine cooling system, and an open position for allowing the flow of coolant fluid through the engine cooling system. Such thermostats are typically closed as long as the temperature of the coolant fluid is below a specified closing temperature, and are open as long as the temperature of the coolant fluid is above a specified opening temperature. The specified closing and opening temperatures may or may not be equal.
It is desirable to monitor the operation of the engine cooling system to determine whether it is operating normally or if the thermostat has failed. What is therefore needed is a system for diagnosing the operation of an engine cooling system to determine its current operational state and detect thermostat fault or failure conditions as they may occur.